Process for preparing aromatic amines



Patented Nov. 12, 1935 UNITED STATES PATENT OFFICE PROCESS FOR PREPARING AROMATIC AMINES No Drawing. Application December 11, 1934, Serial'No. 756,972

7 Claims.

ess for preparing said amines by the reduction of the corresponding aromatic nitrocompounds.

The method commonly described for the preparation of aniline, for example, has comprised the reduction of nitrobenzene by iron or other metal and an acid, such as acetic or hydrochloric acid. It has been known for some time also that aniline and other aromatic amines may be prepared by the reduction of the corresponding nitrocompound by means of iron and water in the presence of a catalyst such as ferrous chloride, aluminum chloride, and the like. Heretofore the quality of the iron employed in these reductions has not been regarded as a matter of great importance, hence the cheapest forms of scrap iron, such as cast iron borings, punchings, and the like were used. Such forms of iron, though attractive for economic reasons, possess certain very objectionable properties. Due to the wide variations in chemical composition and physical states, the material does not lend itself to close chemical control. The actual iron content varies widely and is generally below 95%. Due to factors at present obscure, the activity of the iron heretofore employed is subject to wide and unpredictable variations, which fact necessitates sampling, preliminary testing and frequent rejection of the material supplied. Moreover, although cast iron borings, punchings, and the like are frequently employed because they are generally readily available, this availability is not always the case.

The present invention has for its object a new and improved process for preparing aromatic amines. A further object is a process for preparing aromatic amines which lends itself to careful chemical control. A still further object is a process for preparing aniline by means of materials which are consistently pure, highly reactive, and readily available. Other objects will be apparent as the invention is hereinafter disclosed.

The foregoing objects may be accomplished by taking advantage of certain hitherto unappreciated possibilities of a well known form of iron.

We have found that comminuted sheet iron or steel, which has a large surface and is therefore readily attacked, produces a much smoother reaction than cast iron borings. Comminuted ordinary sheet iron may be used with advantage for this purpose. but we prefer to use tinned sheet iron, the-surface of which has been only partly freed from tin.

We have found that tinned ferrous sheet metal, such as the tin-plate employed in the manufacture of the so-called tin-cans, containers, and the like, is a consistently pure form of iron for our purpose which, if comminuted and partly detinned, constitutes an extraordinarily active reducing agent for preparing aromatic amines from the corresponding nitrocompounds. The reason for this unexpected activity is obscure, but may possibly be due to an electrolytic effect between the tin and the iron.

It is well known, for example, that sheet iron having an unbroken tin coating is very resistant to rust, but that, when the tin coating is broken at any point, rusting proceeds from this point at a very much increased rate, due to someelectrolytic action between the contacting metals.

Whether a similar action is the cause of the reactivity of partly detinned sheet ferrous metal or not can not be definitely established. The fact remains that such material has a much greater reductive power than the usual forms of iron.

The material for the purpose of this invention may be obtained in the form of sheets, if desired. We find it convenient, however, to use scrap tinned plate, since it is more readily comminuted to the required dimensions. This so-called tin scrap must be at least partly detinned either chemically, by well known methods, or mechanically, as by rumbling the tin scrap in a ball mill. Unless the tin is partly removed, however, the tin-plate is not a properly active form of iron for this type of reaction, due to the protective action of the unbroken plating.

The material so prepared possesses very desirable properties. Its purity is consistently above 98% Fe, its reactivity is unexpectedly high, and its reductive power in the preparation of aromatic amines from the corresponding nitrocompound, as compared to'that of the iron heretofore employed in the art, is very high. The remarkable reductive powers of this material may be seen from the following data for the reduction of 500 grams of nitrobenzene with 550 grams of iron and 1500 grams of water, in the presence of 5.5 grams of ferrous chloride. Iron from cast iron borings, ground to pass an 18-mesh screen, required two hours for complete reduction.

In contrast to this, partly detinned tin-plate, comminuted to pass a I l-mesh screen, produced an uncontrollably violent reaction, while a similar material, comminuted to pass a 6-mesh screen, required only one and a quarter hours.

For a given particle size, as determined by screening, the reactivity of the partly detinned sheet iron is much greater than that of cast iron borings or similar forms of iron, as is readily seen from the violence of the reduction mentioned above, in which the 14-mesh material was employed.

From these data it will be apparent that the remarkable reductive powers of partly detinned sheet ferrous metal are applicable not only to the preparation of aniline from nitrobenzene, asois illustrated above, but in general to the preparation of all types of primary aromatic amines from the corresponding nitro-c'ompounds. Thus, by the same general procedure, the following amines, which are cited by way of example, may be produced from the corresponding aromatic nitrocompounds: aniline, ortho-and para-toluidines, the various xylidines, alpha and beta naphthylamine, and in general any primary aromatic amine from they corresponding nitrocompound, pro vided the nitrocompound does notcontain a functional group other than the nitro group which is attacked under the conditions obtaining in this reduction. 7

It will be apparent to those skilled in the art that the present invention can be employed with any of the well known iron-reduction catalysts, such as hydrogen chloride, ferrous chloride, ferrous sulfate, chromium chloride, cobalt chloride, aluminum chloride, and the like. It is understood that the words tinned plate and tin-plate are used interchangeably in these specifications and claims, and are to be construed as referring to sheet ferrous metals, such as iron and steel, which have been coatedwith tin.

Having now disclosed our invention in detail, it is to be understood that many variations can be made without departing from the spirit of the I invention. We therefore intend to: be limited only in accordance with the following patent claims.

We claim: 1. The process of preparing primary aromatic amines, which comprises the treatment of the corresponding aromatic nitrocompound with comminuted sheet ferrous metal, in the presence of water and an iron reduction catalyst.

2. The process of preparing primary aromatic amines, which comprises the treatment of the corresponding aromatic nitrocompound with ferrous 10 metal the surface of which is partly covered by tin, in the presence of water and an iron reduction catalyst.

' 3. The process of preparing primary aromatic amines, which comprises the treatment of the corresponding aromatic nitrocompound with comminuted sheet ferrous metal the surface of which is partly covered by tin, in the presence of water and an iron reduction catalyst.

4. The process of preparing primary aromatic g0 amines, which comprises the treatment of the corresponding aromatic nitrocompound with partly detinned, comminuted tin-plate, in the presence of water and an iron reduction catalyst.

5. The process of preparing alpha-naphthylamine, which comprises the treatment of alphanitro-naphthalene with partly detinned, comminuted tin-plate, in the presence of water and an iron reduction catalyst.

6. The process of preparing para-toluidine, 3 which comprises the treatment of para-nitrotoluene with partly detinned, comminuted tin-plate, in the presence of Water and an iron reduction catalyst.

'7. The process of preparing aniline, which comprises the treatment of nitrobenzene with partly detinned, comminuted tin-plate, in the presence of water and an iron reduction catalyst.

' FORD H. McBERTY.

KENNETH C. SIMON. o 

